Roof antennas for vehicles having a base plate on which antenna elements or modules are arranged are known. In order to protect these elements against external influences such as water, mechanical influences (particularly streams of air) and the like a cover (also called protective hood or cap) is provided. The cover of a roof antenna can be fastened in known manner on or at the base plate by means of several screws that are vertically screwed into complementarily threaded bosses in the cover from below near the outer edge of the base plate or the cover. This method for fastening the cover has the disadvantage that the number of the screws and thus the fabrication efforts for mounting are relatively high (usually five to seven or more screws) and that the cover construction is complex and difficult as far as the design is concerned. Visually disturbing marks (sink marks), caused by plastic contraction, particularly in the region where the vertical bosses merge with the visible outer surface of the cover, cannot be avoided. Moreover, once the roof antenna is installed on the vehicle, it is impossible to simply remove the cover and to exchange it, since then the screws are covered from below by the vehicle body and are only accessible if the antenna is taken off.
The method shown in FIG. 8 for fastening the roof antenna cover, where the disadvantages mentioned above are avoided, is known. There, rather than a plurality of screws, only one central screw is used to secure the cover to the base plate from above (if necessary by providing an additional spacer between the cover and the base plate, as shown). Thus, the screwing of the cover onto the base plate is less complex, the construction of the cover is simpler and sink marks do not pose any problem, since no further screwing bosses in the cover are required. With this kind of fastening method, the cover can be simply unmounted even when the roof antenna is installed on the vehicle, since the screw is freely accessible from the outside.
Such fastening means that are visible from the outside, freely accessible and unprotected, are disadvantageous, however, since the screw head that is visible from the outside and the recess in the cover required, in which the screw head is inserted, considerably disturb the visual impression of the roof antenna as a design element and are therefore undesirable. Moreover, such visible and freely accessible fasteners incite unauthorized persons to remove the roof antenna or the cover without permission, either for purpose of theft or vandalism. Furthermore, there is a certain risk that humidity might get into the inside via the opening in the antenna cover, particularly if the screw head is countersunk in a recess in the cover and rain water accumulates in this recess.
Also, dirt that is hard to remove from the cavity accumulates very easily in such recesses and interferes with access to and/or the operation of the fastener. Thus, if dirt accumulates for example in the hex or torx socket of a cylinder screw, the use of a corresponding tool is no longer possible.
The roof antenna itself can be usually fastened on the body of a vehicle by means of a threaded stem formed on the bottom face of the base plate. The stem extends through a complementarily shaped hole in the vehicle body when the roof antenna is put on the vehicle body from above or from the outside, and afterward a special annular gear nut is screwed on the stem from below or from the inside of the vehicle. Additionally, other versions are known, where a screw with an adequate plain washer for fastening the roof antenna from below is used instead of the nut, as can be seen in FIG. 8. These fastening methods have the disadvantage that the roof antenna, when installed from above, has to be screwed on from the inside of the vehicle body, so that a change of position of the installer is necessary so that the installation process thus becomes unnecessarily laborious, or so that even two installers might be required. Additionally, when the roof antenna is to be removed at a later date, the roof lining in the passenger compartment has to be removed for access to the screws; a fact that unnecessarily complicates later removal of the roof antenna.
A simple and known possibility for fastening a roof antenna to a vehicle body by simply screwing it on from above is shown in FIG. 9. The screw head can be more or less countersunk in the cover. The screw extends to the sheet metal of the vehicle body and is screwed into a thread in the sheet metal. In the simplest case, only a round hole in the sheet metal is required and the screw autonomously forms its thread when the roof antenna is screwed on. Similarly to FIG. 8, an additional spacer may serve for reducing the required screw length, particularly if the screw head is to be provided within the area of the cover surface. Instead of a central screw, several such screw connections might be used. The disadvantages, however, of such a fastening means, which is visible from the outside, freely accessible and unprotected, are the same as the disadvantages already described above.